Lowering the dielectric constant of an interlayer dielectric film is an important challenge to be met for making a semiconductor device faster and reduce power consumption. Various ideas have been implemented with a view toward lowering a dielectric constant.
In order to lower a dielectric constant of the interlayer dielectric film of a related-art semiconductor device, the following methods have been put forward:
(1) a method for doping a silica film, which is an inorganic dielectric film, with fluorine;
(2) a method for forming an organic dielectric material having a low dielectric constant as a base material; and
(3) a method for intentionally forming a porous film.
However, in the case of the method defined in (1), a silica film can be doped with fluorine on the order, at most, of a few percentages in element proportion, because the heat resistance of the dielectric film is deteriorated. Therefore, there arises a problem of the dielectric constant being lowered by only 10% to 15% from the dielectric constant of the related-art silica-based interlayer dielectric film.
In the case of the method defined in (2), the moisture resistance of the base material is considerably deteriorated as compared with that of the related-art silica-based interlayer dielectric film, because the base material is an organic material, thereby leading to occurrence of a problem of a decrease in reliability of a semiconductor element.
In the case of the method defined in (3), since a porous structure is random, the mechanical strength of the interlayer dielectric film will be deteriorated remarkably. Hence, the semiconductor element is vulnerable to fracture when being packaged, which is responsible for the decrease in the reliability of the semiconductor element.
In many cases, a porous structure is not closed. If the porous structure is not closed, the moisture resistance of the interlayer dielectric film will be decreased remarkably, which in turn induces a decrease in the reliability of the semiconductor element.
Moreover, as further miniaturization of the semiconductor device and realization of a still higher packing density are pursued, inter-wiring capacitance and inter-wiring-layer-capacitance pose serious problems.
As mentioned above, the related-art dielectric film suffers from a problem of the inability to sufficiently reduce a dielectric constant and a problem of insufficient mechanical strength.